// @(#)PreemptPriorityQueue.java   12/2003
// Copyright (c) 1998-2003, Distributed Real-time Computing Lab (DRCL) 
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package drcl.inet.core.queue;

import java.util.Vector;
import drcl.data.*;
import drcl.util.queue.*;
import drcl.comp.*;
import drcl.comp.queue.QLogic;
import drcl.net.*;
import drcl.inet.InetPacket;

/**
 * PreemptPriorityQueue is the same as {@link PriorityQueue} except
 * that an arrived higher-priority packet can preempt (and drop)
 * a lower-priority packet when the queue is full.
 */
public class PreemptPriorityQueue extends PriorityQueue
{
  public PreemptPriorityQueue()
  { super(); }
  
  public PreemptPriorityQueue(String id_)
  { super(id_); }
  
  /**
   * Enqueues the object at the end of the queue
   * @return the object being dropped due to the enqueue; null otherwise.
   */
  public Object enqueue(Object obj_)
  {
    Packet p_ = (Packet)obj_;
    int psize_ = isByteMode()? p_.size: 1;
    int level_ = classifier.classify(p_);
    if (level_ < 0 || level_ >= qq.length)
      level_ = qq.length-1; // lowest priority
    
    int oldSize_ = currentSize;

    if (currentSize + psize_ > capacity) {
      // need to drop

      // already lowest priority or no capacity in the queue of
      // the same level
      if (level_ == qq.length-1
        || qq[level_].getSize() + psize_ > capacity) {
        if (isGarbageEnabled()) drop(p_, "buffer overflow");
        if (qlogics != null && qlogics.length > level_
            && qlogics[level_] != null)
          qlogics[level_].dropHandler(p_, psize_);
      }
      else {
        String advice_ = qlogics != null && qlogics.length > level_
            && qlogics[level_] != null?
            qlogics[level_].adviceOn(p_, psize_): null;

        if (advice_ != null) {
          if (isGarbageEnabled()) drop(p_, advice_);
        }
        else {
          // enqueue the new pkt and preempt lower-priority pkt
          currentSize += psize_;
          if (isByteMode())
            qq[level_].enqueue(p_, psize_);
          else
            qq[level_].enqueue(p_);

          for (int i = qq.length-1; i>level_; i--) {
            VSFIFOQueue q = qq[i];
            if (q.isEmpty()) continue;

            QLogic logic_ = qlogics != null && qlogics.length > i?
              qlogics[i]: null;

            while (!q.isEmpty()) {
              Packet tmp_ = (Packet)q.remove(q.getLength()-1);

              int tmpsize_ = isByteMode()? tmp_.size: 1;
              currentSize -= tmpsize_;
              if (isGarbageEnabled()) drop(tmp_, "preempted");
              if (logic_ != null)
                logic_.dropHandler(tmp_, tmpsize_);
              if (currentSize <= capacity) break;
            }
            if (currentSize <= capacity) break;
          }
        }
      }
    }
    else {
      // put pkt to corresponding queue
 
      String advice_ = qlogics != null && qlogics.length > level_
            && qlogics[level_] != null?
            qlogics[level_].adviceOn(p_, psize_): null;

      if (advice_ != null) {
        if (isGarbageEnabled()) drop(p_, advice_);
      }
      else {
        // enqueue the new pkt and preempt lower-priority pkt
        currentSize += psize_;
        if (isByteMode())
          qq[level_].enqueue(p_, psize_);
        else
          qq[level_].enqueue(p_);
      }
    }

    if (oldSize_ != currentSize && qLenPort._isEventExportEnabled())
      qLenPort.exportEvent(EVENT_QLEN, (double)currentSize, null);

    return null;
  }
}
